Tautology

Definition

$t$

A formula or assertion that is true in every possible interpretation

Facts

$\forall$ proposition $p$ $p\vee \neg p\equiv t$ $t\vee p\equiv t$ $t\wedge p\equiv p$

$(p\to q)\wedge (p\to r)\to (p\to r)\equiv t$^[The law of transitivity]